1. Field of the Invention
This invention relates to voltage-to-frequency converters and, more particularly, to voltage-to-frequency converters having increased resolution.
2. Prior Art
Conventional integrating voltage-to-frequency converters operating over an output frequency range of 0 to 10 MHz. are limited in their resolution. To obtain increased resolution, a direct solution is to increase the frequency range of output pulses to 0-400 MHz, or .+-.200 mHz. Obviously, operation in these much higher frequency ranges creates significantly more difficult circuit design and fabrication problems than does operation in a 0 to 10 MHz range.
Another solution to increasing resolution in a conventional integrating voltage-to-frequency converter is to use an interpolation type of approach to obtain increased resolution. This approach uses a voltage to frequency converter to obtain, in effect, the most significant bits MSBs for a sample of an original analog input signal. The MSBs are then reconverted to an analog version of the MSBs which are in turn, subtracted from the sample of the original analog input signal to create an analog difference sample signal. This analog difference signal is then converted to a digital format with an A/D converter to create, in effect, the least significant bits LSBs for the sample of the original analog input signal. The information contained in the LSBs can be used to provide increased resolution. However, this type of interpolation method adds complexity because of the need for A/D circuits, sample-and-hold circuits, digital latches, adder/subtractors, etc.